Human Immunodeficiency Virus (HIV-1) is a global threat to public health and poses an unprecedented challenge to drug development. HIV-1 drugs that directly target virus often fail due to rapid emergence of drug resistance. Functional Genetics (FGI) used a proprietary technology, Random Homozygous Gene Perturbation (RHGP) and discovered novel host gene targets that block HIV-1 infection without observable deleterious effect on cell survival. Unlike viral-targets, treatments relying on cellular targets are expected to retain broad spectrum efficacy against all HIV variants including drug-resistant viruses. In addition, by removing the selective pressure on the virus, host targeting circumvents drug resistance development. The identified targets in Phase I studies were validated using a siRNA approach and also shown to be commonly necessary for infection by both CXCR4 and CCR5 tropic HIV1 viruses. These results demonstrate the power of FGI proprietary RHGP technology to identify host targets(s) in human genome that block viral infection and at the same time are non-toxic. In the Phase II proposal, we will develop novel targeted intervention against HIV using monoclonal antibody therapeutics. We will focus on one particular host target, Robo1, which is essential for the life cycle of HIV-1. To this end, we have discovered that Robo1 expression is activated in primary CD4+ T lymphocytes by HIV-1 infection. As a result, Robo1 uniquely appears on the surface of live, viral producing cells. Robo1 antibodies exhibited anti-HIV-1 activity in human PBMC assays. Robo1 thus can be targeted by monoclonal antibodies to block HIV life cycle and/or to eliminate infected cells via normal host defense mechanisms such as antibody-dependent cellular cytotoxicity (ADCC) and/or complement-dependent cytotoxicity (CDC). We will conduct phage-based screening of human scFv libraries to identify antibody candidates that selectively recognize HIV-1 infected but not uninfected cells. These leading scFv candidates will be built out into full- length human IgG1 antibodies and using molecular evolution approach, the binding affinities of lead antibody candidates will be enhanced by several orders of magnitude. Their broad spectrum anti-viral abilities will then be evaluated including direct inhibition of viral replication and/or mediation of ADCC and CDC effects in vitro and efficacy in humanized mice. Antibody lead(s) will be further scrutinized through cell-based, animal-based and tissue cross-reactivity assays. Based on antiviral activities and iterative improvements, we will nominate a lead Robo1 antibody candidate for IND-enabling studies. We believe the concept of selective targeting of HIV- infected cells has exciting prospects and that it is feasible to develop a therapeutic monoclonal antibody against a broad spectrum of HIV isolates. PUBLIC HEALTH RELEVANCE: Most current AIDS drugs target the HIV virus and therefore enable the development of drug resistance through viral mutation. The Phase I project seeks to identify human host targets (as opposed to HIV virus targets) that will prevent the HIV virus from using the host's cellular mechanism for its life cycle. The overall goal of Phase II is to develop Host Oriented Therapeutic antibodies using targets identified from Phase I. These antibodies are expected to be active against all variants of HIV, including those with resistance to current antiviral therapies.